1. Technical Field
The present invention relates generally to filtration media for removing contaminants from streams of air that pass through the filtration media, and, more particularly, to a filtration media comprised of a zirconium hydroxide analog for removing acid gases and an acidified component for removing basic gases.
2. Description of the Related Art
Air purification is of major concern to the military, first responders, and industrial workers. Applications in the field of air purification are often classified into individual protection and collective protection. An example of individual protection is the filtration incorporated into respirators worn by an individual person. Examples of collective protection include air filtration that is incorporated into the air handling system of a space that may be occupied by more than one person, such as a room, vehicle, or building.
Many of the prior art filters contain activated, impregnated carbons to filter toxic chemicals. These impregnated carbons have limited service life after exposure to the operating environment. That is, the filtration performance in removing toxic gases from air passing through the impregnated carbons deteriorates to a point considered unsuitable such that the filter needs to be replaced. Service life is limited by physical adsorption life and reactive life of the impregnated carbons. Physical adsorption life is reduced by adsorption of air pollutants. Reactive life is typically reduced by temperature and amount of water adsorbed by the carbon bed, adsorption or reaction with air pollutants, and any cross-reaction that may occur between or among the media components.
Prior art materials used for military filters typically contain impregnated carbons with the impregnants used to provide protection against acidic or acid-forming gases. These filters typically lack sufficient removal capabilities against several basic or base-forming gases. The term “basic” will be used hereinafter to refer to both basic gases and gases that are basic forming. Similarly, the term “acidic” will be used hereinafter to refer to both acidic gases and gases that are acid forming.
Examples of acidic gas contaminants include, but are not limited to, sulfur dioxide (SO2), hydrogen cyanide (HCN), chlorine (Cl2), hydrogen chloride (HCl) and fuming nitric acid (HNO3). Examples of basic gases include, but are not limited to, ammonia (NH3) and methylamine (CH3NH2).
Other prior art filters, such as those developed under standards employed by the National Institute for Occupational Safety and Health (NIOSH) for applications requiring Chemical, Biological, Radiological, and Nuclear (CBRN) protection, contain impregnants for the removal of both acidic and basic gases. These materials provide substantial broad-spectrum removal capabilities, however, they also show aging due to interaction of the impregnants with one another within the carbon pore structure. That is, the reactive life of these filters is reduced not only by the temperature and amount of water adsorbed by the carbon bed due to the operating environment, but also due to a cross-reaction that occurs between or among the impregnants.
Related prior art filter media includes zirconium hydroxide as a component, which may be expressed as Zr(OH)4. Zirconium hydroxide with the addition of zinc and other metals, along with triethylenediamine (TEDA) has been used to provide removal capabilities against a wide range of toxic acidic and oxidizable gases, such as chlorine, hydrogen chloride, hydrogen cyanide, phosgene, cyanogen chloride, sulfur dioxide, nitrogen dioxide, and the like. One shortcoming of the material, however, is that it provides limited removal of basic forming chemicals such as ammonia, methyl amine, and ethylene oxide.
Other prior art approaches use non-carbon materials for removal of basic gases. This includes use of zirconium hydroxide as a substrate impregnated with sulfuric acid and oxalic acid for ammonia removal. Zeolite H-ZSM-5 also has shown promise as an ammonia and ethylene oxide removal material, and has been demonstrated for military application in the Joint Service General Purpose Mask (JSGPM) program.
Other materials showing promise against basic gases are metal-organic frameworks. Specifically, the metal-organic frameworks or MOFs known as CuBTC and M-MOF-74 (where M stands for cobalt, copper, magnesium, nickel, zinc and/or other metals) have shown substantial removal capabilities. These metal-organic frameworks, however, are not effective at removing acidic gases.
In summary, prior art filtration media generally suffers in applications that require removal performance against a broad spectrum of acidic and basic gases, or the filtration media has a limited service life, or both broad-spectrum removal performance and service life are suboptimal.
Accordingly, there is a need for filtration media capable of removing a broad spectrum of contaminants from streams of air that pass through the filtration media with a satisfactory performance life when exposed to normal environmental conditions of humidity, temperature, and the possibility of cross-reaction within the filtration media.